The circulatory system is the transport path through which nutrients and oxygen are carried to the tissues, carbon dioxide is returned to the lungs and metabolic products are distributed throughout the body. Blood, the carrier of these substances, is comprised of red blood cells, white blood cells, and platelets suspended in plasma. The study of blood rheology enables researches to evaluate the influences of regions of stasis, particle entrainment, red blood cell aggregation, shear rate, drag, etc., on blood flow. An understanding of these factors would provide significant insight into vascular functioning.
There has been considerable prior art interest shown in model tube experiments with flowing suspensions in order to gain a possible insight into vascular functioning. The results have been informative as regards random migration under collision, wall effects, the effect of particle concentration on velocity profiles, etc. Such experiments have generally been performed with abiological materials. For example, one prior art approach employs apparatus for determining the passage of a particle through any selected point on a tube cross-section by measuring the coincidence when a particle blocks two (2) mutually perpendicular light beams. In this approach, the internal diameter of the tube was approximately 11 mm and latex spheres were employed. The distribution of the particles was obtained by counting the particles as represented by the blocking of the two light beams. The disadvantages of this approach involves the macroscopic dimensions, the use of artificial latex spheres instead of actual blood particles, and the need for large sensors to count the particles.
In order to obtain information that is more definitive and applicable to the in vivo flow situation, it is desirable to work with actual blood samples in a state as close to physiological as possible. However, light transmission through normal hematocrit blood, flowing through macroscopic tubes, is so attenuated as to preclude informative measurements.
Light transmission through microscopic volumes of blood has long been the basis of our understanding of microvasculature. Recent advances in manufacturing technology have made capillary tubes of uniform microscopic bore commercially available. While this has extended the range of controlled in vitro experimentation, data acquisition has thus far been limited to net optical density measurements and high speed motion picture filming of particle behavior. Data processing, particularly in the latter case, is extremely laborious and time consuming.